The effect of mechanical activation of nitinol powder on the interaction with hydrogen

Abstract

In this study the effect of high-energy mechanical activation of Ti-Ni powder on the hydrogen interaction has been investigated. High-energy mechanical activation was carried out in a planetary ball mill with an acceleration of 60g. The initial powder has a mixture of phases TiNi (B2) and (B19′), Ti2Ni, TiNi3. The lattice parameters of these phases correspond to literature data. It has been shown that after high-energy mechanical activation a quasi-amorphous phase was formed in a powder. The content of crystalline phases decreases from 100% up to 45%, while the content of the quasi-amorphous phase increases accordingly. It was shown that lattice parameters of phases slightly change for 0.3– 0.5%. The width of all peaks doesn’t significantly changes during the first 10 s of mechanical treatment, but a longer processing time leads to its increase which corresponds to an increase of the defect density. It has been shown that lattice parameters of the TiNi and TiNi3 almost does not change after hydrogenation of studied powders, while the lattice parameter of Ti2Ni increases by 2.5% after hydrogenation; this means that the main interaction of hydrogen in the Ti-Ni system occurs with the Ti2Ni phase. It has been shown that lattice parameters of Ti2Ni-based phase corresponds to the hydrides Ti2NiH0.5 and Ti2NiH0.8 after 30 and 300 s of mechanical activation. It has been obtained that the time of hydrogenation of 90 min is a critical time after which one can observe changing of lattice parameter of studied powders after treatment. The lattice parameter corresponds to the Ti2NiH0.5 hydride after 180 min of hydrogenation. A possible reason may be oxide films formed on the surface during mechanical activation treatments, which broke at long-time hydrogenation.